Field of the Invention
The present invention relates to a technique for detecting an abnormal connection of a reading sensor module in an image reading apparatus that optically reads an original.
Description of the Related Art
A control method regarding the detection of abnormalities in a reading sensor of an image reading apparatus is disclosed in Japanese Patent Laid-Open No. 2004-88564. In Japanese Patent Laid-Open No. 2004-88564, the aim is to provide an image reading apparatus that can easily determine whether there are any abnormalities in either the light source for original image illumination or the CCD sensor for original image reading. As a means for solving the problem, in order to detect abnormalities in the CCD sensor without being affected by the light source or external light, the timing of sampling is made variable in the sample and hold circuit that samples and holds the output signal of the CCD sensor. Then, when the CCD sensor is examined, sampling is performed while the CCD sensor output signal has reset noise. Reset noise is detected if the CCD sensor is normal, and reset noise is not detected if there is an abnormality, and thus a CCD sensor abnormality can be detected by determining whether reset noise is present or absent.
However, the reading sensor of Japanese Patent Laid-Open No. 2004-88564 is based on the premise of a CCD sensor, and reset noise is not externally output from a CMOS sensor, and therefore this technique cannot be applied. Also, the voltage that is output in the reset noise is not stable and fluctuates over time. For this reason, the stable sampling of reset noise including variation of the CDD sensor is not easy.